In this paper, to detect hydrogen sulfide (H2S) gas. the electronic structure, density of states, charge population analysis and electrical conductivity change at room temperature for Zinc oxide decorated graphene sheets (ZnO-GS) nanostructure were studied in detail. The calculations were performed using Density Functional Theory. The results strongly showed that the ZnO-GS nanostructure could be used as a nanosensor to detect H2S gas at room temperature. Based on this set of calculations, H2S adsorption energy on ZnO-GS showed a significant increase compared to the pure graphene sheets. The electrical conductivity of ZnO-GS was significantly changed at room temperature, after adsorption of H2S. Based on these studies, the ZnO-GS nanosensor can be used to detect H2S. Obtained results are in excellent agreement with reported experimental results.